As semiconductor processing technology approaches the limits of traditional CMOS scaling, process integration has become increasingly challenging, and has resulted in diminished rates of performance improvement. Consequently, there is currently considerable interest in the art for chip package stacking solutions, including “system in package” (SiP) and “package on package” (PoP) technologies. Additional performance enhancements and reduced form factors can be realized with the use of three-dimensional integration. Through semiconductor vias (TSVs) are an important key to solutions of this type, since they enable three-dimensional stacking and integration of semiconductor devices.
Frequently, three-dimensional integration involves the face-to-face attachment of die, which necessitates the creation of I/O through die substrates. Typically, this is accomplished by forming deep TSVs through the die, filling the vias to form interconnects, and utilizing solder joints to attach the stacked 3D die to packaged substrates. However, while various methods exist in the art for filling vias, the application of these methods to filling deep TSVs has proven to be less than satisfactory.
In particular, and in comparison to standard interconnect vias, these deep TSVs are very difficult to fill with metal due to their high aspect ratios and the sheer volume of metal required. Thus, electroless processes for plating vias can be slow when applied to TSVs due to the relatively large volumes of metal required. Electroplating methods offer faster via fill and, in many applications, produce a fill of superior quality. However, these methods, in the form in which they are typically implemented, often produce a large metal overburden which can generate considerable stresses on the wafer. Moreover, such an overburden may require extended chemical mechanical polishing (CMP) to remove.